The present invention relates to a sheet heating device in which a sheet is delivered while being heated by a heater disposed in a sheet feed path. More particularly, the invention relates to a sheet heating device suitable for a copying machine.
In general, in various copying machines, in the case where an image formed of thermally molten substances is formed on a piece of sheet such as paper, the sheet is clamped between paper feed rollers and is fed onto a delivery means. In a convection type heating means, air heated by a heater is recirculated and impinged onto the sheet, or in a radiation type heating means, the sheet is heated by radiation heat of the heater. Thereafter, the sheet is clamped and discharged by discharge rollers
However, in the conventional sheet heating device, during heating of the sheet, heated air would be leaked from a cover to heat the paper feed/discharge rollers and the paper feed/discharge rollers would be heated by the radiation heat of the heater. As a result, the sheet would be rapidly heated on the paper feed side. In this case, the thermally molten substances forming the image are boiled to form bubbles, thereby degrading a quality of the image. On the other hand, thermally molten substances are molten by the heat of the discharge rollers and would be adhered to the discharge rollers, thereby forming image damages such as flow and breakdown to deteriorate quality of the image.
Also, in a conventional copying machine, in the case where a latent image formed in a photosensitive-pressure sensitive sheet is transferred to a developer paper to form a visible image, after the sensitive sheet and the developer paper have been overlapped with each other under a pressure, only the developer paper is fed to a heating device. In the heating device, the image is thermally fixed by the operation of a heater and a fan within the heating device.
However, in the heating device, since an inlet into which the developer paper is fed and an outlet from which the developer paper is discharged are always open, the leakage amount of the heated air is increased, so that a heat loss is increased and it takes long time to perform the heating treatment. Also, it is necessary to increase the capacity of the heater, which leads to an increase of the manufacture cost. Also, other instruments located around the heating device are excessively heated. Thus, the conventional heating device suffers from various disadvantages.